The overarching goal of this project is to forward and backward track cancer cell fates and histories using new imaging approaches to redefine cancer evolution and therapeutic escape on the cellular and molecular level. The project will focus on clonal selection, in order to develop a single unifying hypothesis, which can explain a variety of clinical observations including that of primary tumor cell heterogeneity, the propensity for metastases to develop at specific sites, and the differences in therapeutic responses. Current methodologies for studying in vivo clonal expansion and tumor growth have been hampered by the overwhelming challenge of being able to follow the development of distinct cellular lineages from a single common progenitor. By adopting vanguard technologies such as combinatorial expression of multiple fluorescent proteins (Livet et al., 2007, Nature, 450, 56-62), we will be able to perform fluorescent-based lineage tracing of cancer cells in vivo. The overarching goal for this project is to better understand the clonal fates of both tumor cells and their associated stromal cells. The specific aims are thus: 1) to develop, test and validate multicolor tools and reagents to track multiple clonally derived cellular lineages; 2) to determine whether tumor formation, progression and resistance to therapy are characterized by dominant subclones; and 3) to examine whether tumor cells recruit unique subpopulations of host stromal cells to the growing tumor.